The influence of antibiotics on gut colonization.

Animal and human studies have suggested the concept of "colonization resistance" of the gastro-intestinal tract, which can be decreased by administration of antibiotics that inhibit the anaerobic portion of the normal flora of the gut. This effect can be prevented by the production, by resistant members of the flora, of bacterial enzymes that inactivate or destroy the antibiotic in question. Possible changes in the prevailing gut flora and the implications for the incidence of different infecting agents and for antibiotic therapy are discussed.